PITTSBURGH -- It was a night for joy in Pittsburgh, but the victory gained in the National League Championship Series opener could prove to be costly.

The Pirates roughed up Atlanta Braves left-hander Tom Glavin for four runs and four extra-base hits in six innings, but their starter, Doug Drabek, may have gotten the worst of the matchup.

In a 5-1 triumph, Drabek strained his left hamstring while tryin to stretch a run-scoring double into a triple at the end of the sixth inning.

He tried to warm up for the seventh, but was favoring his leg and had to leave the game. If Drabek is unavailable for Game 5 on Monday, the Pirates pitching could suffer should the series be an extended one.

Pirates manager Jim Leyland said the early diagnosis is that the injury "is halfway between a cramp and a hamstring. The trainer felt comfortable that he would make his next start. It's not a pull and not a cramp, but sometimes you wake up tomorrow and it's different from what you thought."

The Braves, who are a combined 0-7 in three NL Championshi Series, never were in the game, which was attended by 57,347, the largest crowd in Pittsburgh baseball history.

After Drabek left, veteran Bob Walk shut them down, with the exception of David Justice's homer leading off the ninth.

Walk's entrance left little doubt that Leyland intends to start left-hander Randy Tomlin in Game 4 at Atlanta.

Leyland relieved with Walk instead of a left-hander because, the manager said, "I thought he'd get the ball over the plate and he did. I felt I wanted to go with the veteran, and I really like Walk against [Sid] Bream."

Drabek and Walk combined to allow only four singles and seven base-runners, one on an error by Gary Redus, until Justice connected.

The Pirates seemed more relaxed than last year, when their stellar outfield, Barry Bonds, Bobby Bonilla and Andy Van Slyke, combined for only five RBI in a six-game loss to the Cincinnati Reds.

Van Slyke was right in form. He batted a mere .195 against left-handed pitching this year but has a .344 career average against Glavine.

Van Slyke homered on a 3-2 breaking ball in the first to "set the tone," according to Bonilla. Then, Van Slyke doubled in the gap in right-center to spark a two-run third.

"It just happens that at this point I happen to hit Tom Glavine better than most left-handers," Van Slyke said. "I'm glad he's not with Los Angeles or some other club not in the playoffs."

The three outfielders, who hit a combined .190 against the Reds last year, were 4-for-9 with three runs scored and three RBI, only two fewer RBI than they had in 63 at-bats during the entire 1990 series.

"I think we're more relaxed," said Van Slyke. "Barry, Bobby and I are focused in a different way this year. We realize the ballclub depends on us."

Bonilla, who followed Van Slyke's double with an RBI single, said: "We talked about being very patient and not getting ourselves out. Last year, we tried to do too much and wound up doing nada. We had a lot of anticipation for this game. We all put our energy in the the right place."

Glavine threw 75 pitches through the first three innings and had to pitch out of a bases-loaded, two-out jam in the first inning and a two-on, none-out jam in the third after the Pirates had scored twice.

"His only problem was that he was behind in the count," Braves manager Bobby Cox said. "His location was off, and he paid the price. His stuff was good, probably better than it's been in the last three or four weeks."

Glavine has given up at least one run in the first inning in seven consecutive starts.

The Braves had only one runner to second base before the ninth, and that one, Mark Lemke, was thrown out trying to reach third after his grounder eluded first baseman Gary Redus and rolled up the right-field line.

"I thought Mark would make it. As it turned out, he was out and we looked bad," said Cox. "But you still have to stay aggressive."

Drabek stayed aggressive on a play that seemed unnecessary: Two were out and Pittsburgh led by four runs.

"The ball was right in front of Doug. It was really his call," said Leyland. "He could see what was happening, and that's why he tried [for third]. That's one of the reasons he was out there tonight as the starter. He only knows one way to play -- bust his fanny."

The Pirates were not placing too much emphasis on their lead, although they agreed winning the first one was important.

"We're not getting overly excited," said Leyland. "We won the first game last year, too."